Paracetamol 'useless' in treating osteoarthritis pain

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Behind the Headlines

Friday March 18 2016

Osteoarthritis is the leading cause of pain in older people

"Paracetamol is next to useless at alleviating arthritic pain," The Times reports. A comprehensive review of existing data suggests paracetamol should not be used in cases of osteoarthritis as there are far more effective treatments available.

Osteoarthritis is now the leading cause of joint pain and stiffness in older people.

The review showed that paracetamol, at any dose, had a very low chance of improving pain linked to osteoarthritis (0-4% chance), despite being advised as the painkiller of first choice in current guidance.

In contrast, the non-steroidal anti-inflammatory drugs (NSAIDs) class of painkillers, such as diclofenac (150mg per day) and etoricoxib (30, 60 or 90mg per day) were found more likely to improve pain (between 95 and 100% likely) and were the top-ranked painkilling drugs.

A potential drawback to NSAIDs is that long-term use can trigger complications such as stomach ulcers, and, in rarer cases, heart failure. If a person is thought to be at risk of stomach ulcers, additional protective medication, such as proton pump inhibitors, may also be prescribed.

NICE, the UK's health watchdog, which issues guidance to doctors, is in the process of updating its guidance on drug management of osteoarthritis. Therefore, it is likely that this latest study will feed into the process.

If you have concerns, speak to your doctor. Do not change prescribed medications without consulting your doctor first – not doing so may damage your health.

Where did the story come from?

The study was carried out by researchers from Universities in Switzerland and Canada, and was funded by the Swiss National Science Foundation and Arco Foundation. Many of the researchers involved in the project reported that they were employed by, or had received grants from, pharmaceutical companies.

The study was published in the peer-reviewed medical journal The Lancet.

The UK media’s reports were generally accurate, but largely ignored the "good news" about NSAIDs and instead focused on debating whether paracetamol should be used for arthritic pain. This is a reasonable line to take due to the large numbers of people who use paracetamol to relieve arthritis pain, both in the UK and around the world.

What kind of research was this?

Osteoarthritis is a condition that causes the joints to become painful and stiff. It is the most common type of arthritis in the UK.

There is no cure for osteoarthritis, but it can be effectively managed. The main treatments for osteoarthritis include lifestyle measures – such as maintaining a healthy weight and exercising regularly – medication to relieve your pain (including paracetamol), and supportive therapies to help make everyday activities easier.

What did the research involve?

The analysis found 74 decent sized RCTs (with over 100 people) comparing different NSAIDS or paracetamol with a placebo to improve osteoarthritic pain. How well the drugs improved joint movement was also assessed.

Included NSAIDs that are available in the UK were:

ibuprofen

diclofenac

naproxen

celecoxib (commonly called a COX 2 inhibitor)

etoricoxib (commonly called a COX 2 inhibitor)

The analysis also included rofecoxib and lumiracoxib – both of which have been withdrawn from the UK market due to safety concerns.

In total, 58,556 people were included in the analysis. Average (median) follow up was 12 weeks, with a large range, from one week to one year.

The researchers used a statistical technique called network meta-analysis. This allows direct and indirect comparisons of drugs. For example, if one study compared paracetamol with a placebo, and a second compared an NSAID with placebo in similar conditions, this technique allows you to estimate the probability that paracetamol works better than the NSAID. Including these indirect comparisons is useful, but not as accurate as trials directly comparing one drug with another, sometimes called "head-to-head" trials. This review included both direct and indirect comparisons.

The final output was a rank of all the NSAIDs, paracetamol and placebo, and an estimate of their ability to achieve a minimum, clinically important, difference in pain. The minimum difference was defined at a set point reduction (-0.37 standard deviations) within the overall spread of pain reductions for each trial.

What were the basic results?

Etoricoxib (60mg or 90mg) and diclofenac (150mg per day, the maximum dose) were very likely to improve pain (between 95 and 100% likely) and were the top-ranked NSAIDS. The withdrawn drug rofecoxib was also similarly ranked.

The bottom of the ranking table was filled with different doses of paracetamol.

For example, the highest-ranked paracetamol dose (3g per day) was linked to only a 21% chance of helping pain to a useful level. Doses less than 2g had only a 4% chance of helping pain, ranking second to last, behind Naproxen 750mg.

How did the researchers interpret the results?

The researchers concluded: "On the basis of the available data, we see no role for single-agent paracetamol for the treatment of patients with osteoarthritis irrespective of dose."

They added: "We provide sound evidence that diclofenac 150mg/day is the most effective NSAID available at present, in terms of improving both pain and function. Nevertheless, in view of the safety profile of these drugs, physicians need to consider our results together with all known safety information when selecting the preparation and dose for individual patients."

Conclusion

This Swiss study reviewed drugs commonly used and recommended to help pain associated with osteoarthritis. Through indirect comparison, it identified those likely to be most effective (diclofenac 150 mg/day) and those that are pretty likely to be useless (paracetamol any dose).

The study looked at a large number of good-sized RCTs – all with more than 100 people – and covered a useful range of NSAIDS. The quality of the RCTs was also assessed and was generally not highly biased, although variable.

However, the review included many indirect comparisons of the drugs, which is less accurate and reliable than direct comparisons. But without more direct comparisons available, this is probably the best we have to go on for now.

The main implication from the study authors' point of view was clear: paracetamol has no place in the pain management of osteoarthritis on its own. This finding jars with the UK's current national guidance that advocates using paracetamol as a first-choice painkiller, alongside other osteoarthritis management.

The fact paracetamol might not be useful in the pain management of osteoarthritis does appear to be recognised by NICE – the watchdog that issues guidance on medicines – although the current guidance, based on 2008 recommendations, advocates its use.

For example, NICE reports that it is in the process of updating the guidance and hints that paracetamol may be less effective than thought in 2008. NICE makes a point of saying on its website that an evidence review on the effectiveness of paracetamol as part of a consultation exercise showed, "reduced effectiveness of paracetamol in the management of osteoarthritis compared with what was previously thought."

The current guideline on pain management in osteoarthritis is due to be updated in September 2016.

In the meantime, if you have concerns about taking paracetamol for pain linked to osteoarthritis, consult your doctor before changing your medications.

It is also important not to overlook the benefits that lifestyle changes, such as achieving a healthy weight and becoming more active, can bring.